I did an informal test some years ago... with H335, which Speer data (my main load book at the time) suggests using a Magnum primer. Middle of the road load of H335 with 55grn bullets, the standard primers turned in not only higher velocity, but smaller variance. I think the big thing with ball powders and Magnum primers is very cold temperatures, and I could see it with a compressed load, or a very big charge in a bigger case than the .223/5.56. I did not test for accuracy, that was not the purpose of my test, and it's very likely things could be different if the charge was at max, or it was 12 degrees... or, conversely, 112 degrees.
My rule of thumb is to just pick a primer that works and stick with it through load development. I've used CCI primers almost exclusively since I started reloading in 1989.